Tseung Kwan O Desalination Plant

Transcription

1 The Hong Kong Institution of Engineers Tseung Kwan O Desalination Plant Ir CHAN Tak Yeung, Thomas Chief Engineer / Consultants Management Water Supplies Department, HKSARG Dr. Srinivas (Vasu) Veerapaneni Desalination Technology Leader Black & Veatch Corporation 19 December 2016

2 Outline Uprising Challenges and Strategic Measures Global Desalination Perspective The Desalination Plant Project Overview of Typical Desalination Plant Design 2

3 Uprising Challenges and Strategic Measures 3

4 Is Hong Kong a WATER-SCARCE city? 4

5 Water Rationing in the 1960s 5

6 Three-pronged Supply Dongjiang Water Seawater for Flushing 274mcm (22%) Local Yield 199mcm (16%) 2015 Demand 1245mcm Dongjiang Water 772mcm (62%) Local Yield Seawater 6

7 WATER SECURITY the capacity of a population to safeguard sustainable access to adequate quantities of acceptable quality water for sustaining livelihoods, human well-being, and socio-economic development, for ensuring protection against water-borne pollution and water-related disasters, and for preserving ecosystems in a climate of peace and political stability. (UN-Water, 2013) 7

8 Climate Change Is Happening Taiwan: April 2015 California, USA: April 2015 Thailand: July 2015 Photo source: Hotblack/Morguefile Who s Next? 8

9 How Sensitive is our Water Resources? 9

10 How Sensitive is our Water Resources? 10

11 Hong Kong s Challenge in Water Supply Fluctuating local yield and Donjiang water supply due to climate change Increasing water demand and arising from population and economic growth Keen competition for the Dongjiang water resource 11

12 Total Water Management Demand Management - Water Conservation Supply Management - New Water Sources 12

13 Water Conservation 2% 5% 8% Non-domestic 31% Water Conservation Starts from Home School Talk Roving Exhibition Water Efficiency Labelling Scheme (WELS) Total Water Consumption Save Water. Cherish the World Mobile Showroom Flow Regulator Water: Learn and Conserve Teaching Kit for Liberal Studies 13

14 Water Conservation 2% 5% 8% Non-domestic 31% Total Water Consumption Best Practice Guidelines for Catering Hotel Laundry Industry 14

15 New Water Sources Seawater for Flushing Three Pronged Supply Dongjiang Water Local Yield Reclaimed Water Water Reclamation (~1.5%) Desalination (6%) Grey Water Grey Water Recycling Recycling (~0.5%) Water Reclamation (2%+) Grey Water Recycling (~0.5%) Local Yield (10-25%) Seawater Desalination (5% - 10%) Seawater for Flushing (26%) Six Pronged Supply Dongjiang Water (41-56%) Note: Chart drawn based on average local yield of 295mcm Proposed Desalination Plant 15

16 Global Desalination Perspective 16

17 Global Desalination Trend Proven: 150 countries have installed desalination plants around the world 17

18 Desalination Technologies Currently Available Primarily two types: Thermal Desalination Membrane Desalination 18

19 Thermal Desalination Principle of operation Evaporate water and condense the vapors Oldest desalination technology One of thermal technologies - Multi-Stage Flash (MSF) B&V

20 Lok On Pai Desalination Plant Commissioned in October 1975 Adopted multi-stage flash distillation Decommissioned in 1982 due to high operation cost. 20

21 Membrane Desalination Reverse Osmosis (RO): Principle Start with equal volumes of fresh water and saline water Natural osmosis Osmotic equilibrium (a) (b) (c) (d) Reverse Osmosis P osmotic pressure Fresh water Saline water Fresh water Saline water water water Semi permeable membrane Pure water migrates from low conc. vessel to high conc. vessel Flow stops when hydraulic head on high conc. vessel is equal to solution s osmotic pressure If external P greater than osmotic pressure is applied, Reverse Osmosis occurs (desalination). 21

22 Examples of SWRO Plants, Aus Melbourne desalination plant, Australia Source: Suez Environment Source: Veolia Gold Coast, Australia 22

23 Seawater Desalination by RO New water source not susceptible to climate change Latest reverse osmosis technology 23

24 The Desalination Plant Project 24

25 The Proposed Desalination Plant 2007 Pilot Plant Study confirmed technical feasibility of desalination technologies as a reliable freshwater source 2008 The HK Government promulgated the Total Water Management Strategy which recommended seawater desalination as a new alternative water source 2015 Funding was approved from the LegCo s FC in Jun Environmental Permit was granted by EPD Feasibility study of developing desalination in HK. Pilot Plant Study commenced in Planning and investigation study confirmed the technical and environmental viability of constructing a seawater reverse osmosis desalination plant at TKO Area 137 Nov 2015 Investigation Review, Design and Construction Consultancy Agreement for the first stage of the desalination plant commenced. 25

26 Site Selection Considerations High turbidity in the western waters due to tidal effects in the Pearl River Delta TKO Area 137 is currently a public fill bank zoned Other Specified Uses (Deep Waterfront Industry) Environmental impacts assessed to be acceptable Strategic supply network to other parts of the territory Oceanic current with stable seawater quality in the eastern waters 26

27 The Proposed Desalination Plant Existing TKO fresh water primary service reservoir TKO Area km long fresh water trunk main to convey the fresh water produced at the proposed desalination plant Tseung Kwan O Desalination Plant -First Stage: 135 MLD = ~5% of the daily fresh water demand in HK -- Second Stage: expansion to 270 MLD = ~10% of the daily fresh water demand in HK 350m Submarine outfall 250m Submarine intake 27

28 Overview of Typical Desalination Plant Design 28

29 Seawater RO Process Schematic 29

30 Intake One of the important components of the desalination plant. In fact, treatment starts with a well designed intake Two types of intakes possible: Open intake or Subsurface Intake Subsurface intake high water quality, but not always feasible Submerged open intake selected for the project due to its feasibility Most commonly used around the world Capable of providing large flows Good pretreatment essential as water quality is influenced by many factors Off the littoral zone of the coast to minimize environmental impacts Low influent velocity to prevent impingement 30

31 Open Submerged Intake Open submerged intake at Fujairah, UAE 31

32 Intake at Sydney Desalination Plant 2 tunnels (2.5 km long and 3.4 m diameter) Source: Veolia 32

33 Open intake (submerged pipe, tunnel on land); Gold Coast 2 tunnels (2.2 km influent and 2 m effluent); 2.8 m ID Source: Veolia 33

34 Environmental Considerations for Intake Seawater Intake Submarine pipe to be constructed by micro-tunnelling Design of intake structure to minimise potential impingement and entrainment of fish and larvae Intake Overseas Example (Perth Desalination Plant, Australia) Intake structure of Perth Desalination Plant, Australia (Source:Water Corporation) 34

35 Environmental Considerations for Outfall Discharge Diffusers Submarine pipe to be constructed by micro-tunnelling Rapid dilution of brine to ambient level Confined mixing zone resulting in minimal impact to seawater quality Marine life around brine discharge diffuser of Perth Desalination Plant, Australia (Source:Water Corporation) 35

36 Intake and Outfall of TKO Desalination Plant 36

37 Objectives of Pretreatment Biofouling control Remove turbidity, suspended solids RO membranes are good at removing dissolved constituents. Particulate material can plug up membranes Address the following if present Oil and grease RO membranes are not tolerant Algae Can plug up pretreatment and foul RO membranes Typically, efficacy of pretreatment is measured in terms of silt density index (SDI) However, not all foulants captured by SDI 37

38 Biofouling Control Most common issue for open intake system Shock chlorination most widely practiced Newer practices being tested Change in ph (if feasible for offshore line also) Biofilm monitors Use of newer oxidants that do not damage membranes such as chloride dioxide Use of biocides such as DBNPA* Osmotic backwash of RO membranes *2,2-dibromo-3-nitrilopropionamide 38

39 Pretreatment - Traditional Pressure filters at Perth SWRO Source: water Corporation Coagulation + Filtration (Perth, Ashkelon, Fujairah, Sydney, Gold Coast, etc.) Clarification used as necessary (Trinidad, Singapore, Hamma) Second stage filtration is also used in some facilities (Okinawa, Eni Gela-Sicily) Most commonly used coagulant is iron salt Attributed to broader ph range, discharge limitations Polymer Almost all facilities used it at some point; Continuous usage not preferred can irreversibly damage RO membranes Iron coagulants have lower solubility over a broad ph range compared to Al 39

40 Recent Pretreatment Configurations In-Filter DAF at a SWRO facility Source: Black & Veatch Singapore Coagulation, flocculation, dissolved air flotation/filtration (DAFF) to address algae and oil & grease Barcelona, Spain Coagulation, flocculation, DAF, two stage filtration Beckton, UK Coagulation, flocculation, lamella clarifiers, pressure filters and UF Fujairah II coagulation, flocculation, DAF and media filtration Additional processes primarily to address severe water quality issues 40

41 Algae Requires use of DAF Algal blooms occur periodically Need for treatment dependent on degree of reliability needed and also type and concentration of algae Not all are created equal Variations in morphology could have significant implications for treatment Not all algae concentrations can be estimated by chlorophyll measurements Dinoflagellates could be as large as 100 um and contribute minimally for chlorophyll Source: Harmful algal blooms in coastal upwelling systems, Oceanography,

42 Microfiltration/Ultrafiltration (MF/UF) pretreatment MF/UF as SWRO pretreatment on the rise They are polymeric membranes with absolute pore sizes; Primary benefits No coagulant needed for several, depending on water quality Consistently good water quality Design issues Ability to deal with varying water quality Strainers (type and size) to be selected carefully Algae Interchageability between different suppliers 42

43 MF/UF pretreatment Cost still an issue Membrane life and replacement costs Largest plants with MF/UF are procured under alliance style agreement or DBO contractor has a UF product Adelaide, Perth II Alliance style DBO plants in Australia Tuas II, singapore; Magta and Tlemcen, Algeria and Tianjin china DBO contractor's own the product 43

44 UF pretreatment at 318,000 m3/day (84 MGD) SWRO Source: Hyflux 44

45 Salt passage (%) & Membrane Cost ($/gallons/day) Element productivity (gpd/ft2) Reverse Osmosis Primary process for removal of ions Significant developments in membranes over last few decades Salt passage Membrane Price/Flow Productivity (gpd/ft2) Year Reference: Based on data by Truby et al., 2007 In other words, an element with today s rejection and permeability would have cost 150 times more 30 years ago 45

46 RO Design parameters Recovery Percent of water converted to permeate Flux Quantity of water pushed through unit membrane area Skid Size/Pumping arrangement Number of passes how many times the water is treated Energy recovery devices 46

47 Second pass Typically required to meet specific water quality goals Boron concentration typical reason outside US WHO guideline revised from 0.5 mg/l to 2,4 mg/l. 2 nd pass operated at ph of ~10 to convert uncharged boric acid to charged borate Bromide Formation of brominated DBPs when the desalinated water is mixed with other water sources TDS limits (Chloride, sodium, etc.) Examples: Perth: 90% of the SWRO permeate treated by 2 nd pass 0.1 mg/l bromide limit; Recently relaxed to 0.2 mg/l Ashkelon 100% of the SWRO permeate treated by additional passes 20 mg/l chloride and 0.4 mg/l boron limits Tuas 80% of SWRO permeate at ph of 10 boron limit of 0.5 mg/l Concentrate from second pass typically recycled to SWRO feed 47

48 Boron speciation B rejection 1 st pass 2 nd pass Source : Dow chemical 48

49 Permeate collection for second pass treatment Consider taking permeate from both ends of pressure vessel Permeate from lead end of membrane can bypass second pass treatment Permeate from lag end (higher concentrations of constituents) further treated by second pass Depending on the water quality requirements, elements separated (permeate tube blocked) after 2 or 3 elements 49

50 Permeate conc Permeate 1 Permeate 2 Feed conc Feed water to second pass Permeate from lag elements of the SWRO system could be used as feed to second pass RO Feed Concentrate to waste Feed Permeate1 to post treament Permeate2 for further treatment Good quality - to post treatment Poor quality (wrt B) send to second RO To post treatment concentrate to waste 50

51 RO of TKO Desalination Plant 2 passes RO to achieve the freshwater quality objectives:- Parameter Value Boron 1.0 mg/l Bromide 0.2 mg/l Low bromide concentration to ensure that disinfection byproduct formation won t increase when this water is blended with other water that has organic carbon 51

52 Energy Recovery: Two types of devices to recovery energy I: Hydro-Mechanical Conversion Hydraulic energy in concentrate is converted to mechanical and then back to hydraulic energy Pelton Wheel TurboCharger HP PUMP PELTON TURBINE MEMBRANES II: Positive Displacement Hydraulic energy in concentrate is transferred to feed water directly Work Exchanger Pressure Exchanger Other devices HP PUMP BOOSTER PUMP PX MEMBRANES 52

53 Post-treatment RO permeate is corrosive low ph, low alkalinity, low TDS, low hardness, etc. Typical post-treatment: adjustment of ph, alkalinity and hardness. Target: match ph to that in distribution system have reasonable alkalinity, positive LSI and reasonable CCPP Raising ph: If feed water was acidified, degassify to remove CO2. Add NaOH or Lime Typical chemicals: Lime, NaOH, CO2. Also, use of corrosion inhibitors. Soda ash not so common Calcite filters also an option 53

54 Green Energy Initiative Use of Landfill Gas from South East New Territories (SENT) Landfill Processed gas from SENT available at night time On depletion till around 2030 Technical and financial viability being explored SENT Landfill 54

55 Ultimate Project Objective: Moving Forward A state of the art desalination facility that provides a strategic water source to Hong Kong at optimal cost 55

56 Save Water for the Future Every Drop Counts Thank You